This invention relates to a process for the preparation of a sterilized liquid composition based on casein, more especially a composition adapted for oral or enteral administration.
For the preparation of a sterilised, casein-based enteral composition having a shelf life of up to 12 months, due to the presence of casein, the composition has to be heat-treated for at least 3 minutes at 130.degree. C. This is because the heat-resistant proteases in milk precipitate with acidic casein during its preparation at the isoelectric point (pH 4.6). Because these proteases are not totally deactivated by heat treatment, they cause proteolytic degradation of the casein and leave the end product with a bitter taste, causing it to coagulate after storage for 2 to 6 months. This proteolytic degradation of the casein depends on the concentration of protease in the casein used. Now, a conventional ultra-high-temperature (UHT) treatment of the casein, i.e., for 3 to 5 seconds at 148 or 150.degree. C., which is sufficient to guarantee complete sterility, it not sufficient for completely inactivating the small quantities of residual protease which are difficult to detect by analytical techniques. Accordingly, a more severe heat treatment, i.e., 5 minutes at 130.degree. C., has to be applied. However, a heat treatment as severe as this results in the formation of lysinoalanine (LAL) in a quantity of up to 1800 mg/kg protein and in blockage of the lysine by as much as 20%. The presence of high concentrations of lysinoalanine (LAL) can pose problems of toxicity while blockage of the lysine results in a nutritional loss.
Accordingly, the object of the present invention is to provide a process for the preparation of a sterilized caseinbased composition in which the proteases are deactivated, containing only very low concentrations of LAL (150 to 170 mg/kg protein), and where there is no blockage of the lysine.
This object is achieved by the process according to the invention.